There has long been a need for devices for the continuous production of sandwich composite elements at high production rates. Oscillating mixing heads have hitherto been known from the prior art for the continuous production of sandwich composite elements. The mixing head performs an oscillating movement over the width of a lower outer layer and applies the still liquid reaction mixture to the lower outer layer by means of a casting rake or fan/spoon nozzle which is arranged at a right angle relative to the mixing head and parallel to the lower outer layer.
The mixing head is fixed to a guide rail, the so-called portal, above the lower outer layer and is accelerated with the aid of electric motors and slowed down before the reversal points. The raw materials for foaming are fed to the mixing head via flexible hose lines. Furthermore, in some cases hydraulic or pneumatic hoses lead to the mixing head. The raw materials for foaming are introduced into the mixing head via nozzles and are mixed.
The reaction mixture then flows into the casting rake and emerges through regularly spaced bores. As a result of the length of the casting rake and its bores, as well as the oscillating movement of the mixing head, distribution of the reaction mixture obliquely to the production direction is achieved.
After application, the reaction mixture foams and rises to the upper outer layer. During the foaming process it bonds the two outer layers before the foam solidifies and cures.
This production process is limited in terms of manufacturing technology as regards the production rate. Even if sufficiently strong motors, guide rails, hoses, mixing heads and casting rakes or fan/spoon nozzles were used, the reaction mixture would be carried beyond the edges of the outer layers at the reversal points owing to excessively high centrifugal forces. According to the prior art, production rates of more than 15 m/minute cannot be achieved in the continuous production of sandwich composite elements with this application technique.
The technique of increasing the production rate to up to 60 m/minute by means of stationary mixing head technology and rigid delivery systems is sufficiently well known. This process is called US technology. US technology (high-speed machines) consists substantially of three identical metering lines with separate feed and separate mixing heads and delivery systems. However, this technology does not have a distributor head. This process further has the disadvantage that the reaction mixture emerging from each of the individual mixing heads can also be subject to different physical conditions as regards pressure and temperature, and this manifests itself in the resulting foam as reductions in product quality, such as, for example, uneven surface, smaller cells, different thermal conductivity values due to punctually different reaction kinetics.
EP 1 857 248 A2 solves that problem by not providing every discharge line with a separate mixing head. Rather, only a central mixing head is provided, via which a plurality of delivery lines are fed.
WO 2008/018787 A1 relates to a device for applying a viscous mixture to a surface by means of one or more outlet openings which are fed by a feed element. The specification relates further to a process for the production of an insulating element, comprising the steps of applying a viscous mixture which forms a foam on a substrate layer, the foam subsequently being crosslinked and the foam layer optionally being further coated. A mixing head 3 is supplied with raw material with components from supply pipes 1 and 2. Via a rigid main pipe 8, a casting rake 6 is controlled by a plurality of intermediate webs 5 via a sub-distributor 4. The casting rake is accordingly rigidly connected to the mixing head and can only be moved to the left or right together with the mixing head in order to allow the application region to be adjusted as a whole to the correct position relative to the substrate. Moreover, cleaning of the system is very complex.
WO 2008/104492 A2 discloses a process for the production of composite elements, wherein the application of the liquid starting material for the isocyanate-based rigid foam is carried out by means of a stationary pipe which is arranged parallel and at a right angle to the direction of movement relative to the outer layer and is provided with bores.